When Snakes Fly

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The worst nightmare of ophidiophobes, people with a phobia of
snakes, may have just been realized. Scientists have captured
footage of "flying" snakes, explaining how five related snake
species stay airborne for up to 79 feet.

The acrobatic arboreal snakes, all in the genus Chrysopelea, use
what's known as gliding flight to sail from tree to tree in their
Southeast and South Asia habitats.

The new research, presented today at the American Physical
Society Division of Fluid Dynamics meeting in Long Beach,
explains how the snakes accomplish their seemingly improbable
feat.

"The snake isn't defying gravity or doing something out of the
blue," project leader Jake Socha told Discovery News. "It's the
magnitude of the forces that are somewhat surprising. Given that
this is a snake, and its cross-sectional body shape is more like
a blunt shape than a typical streamlined wing, we wouldn't have
expected such good aerodynamic performance."

Socha, a Virginia Tech biologist, and his team launched the
flying snakes from an over 49 foot tower and recorded the snakes'
every move to the finest detail.

The scientists, whose work has been accepted for publication in
the journal Bioinspiration & Biomimetics, next
developed a mathematical model to explain how the snakes use
gliding flight to travel over such long distances.

"The snake creates lift using a combination of its flattened
cross-sectional shape and the angle that it takes to the oncoming
airflow, known as the angle of attack," Socha explained.

To take off from a tree branch, for example, these snakes will
drop the front of their bodies to create a "J"-shaped loop before
jumping and accelerating upwards. That motion hurls the snake
into the air.

The researchers determined that the airborne snakes never reach
an "equilibrium gliding" state, when the forces generated by the
snakes' undulating bodies exactly counteract the force pulling
the animals down. The snakes did not just immediately fall to the
ground either.

Instead, "the snake is pushed upward -- even though it is moving
downward -- because the upward component of the aerodynamic force
is greater than the snake's weight," Socha said.

"Hypothetically, this means that if the snake continued on like
this, it would eventually be moving upward in the air -- quite an
impressive feat for a snake," he added. "But our modeling
suggests that the effect is only temporary, and eventually the
snake hits the ground to end the glide."

The new model additionally helps to explain the gliding technique
of many other species, including certain mammals, frogs, lizards,
snakes, ants, fish and squid.

In the future, the research might lead to improved micro-air
vehicles, small unmanned and often autonomous flying machines
that could duplicate the energy-efficient gliding flight method
of the animals.

Greg Byrnes, a postdoctoral fellow in the University of
Cincinnati's Department of Biological Sciences, told Discovery
News that the study is "likely the most conclusive to date piece
of evidence against the long-held idea that animal gliders act
much like paper airplanes -- accelerating to an equilibrium and
gliding steadily. And (it) confirms some of our work with gliding
mammals."

"It's really remarkable that an animal that, at first glance,
possesses a body plan that seems so ill-suited to gliding can not
only support its body weight with aerodynamic forces, but
actually create a surplus of these forces," Byrnes added.

Socha likens a snake to a rope, "and that's a pretty bad starting
place to be if you want to design a glider," he said. "Evolution
discovers some pretty unusual ways of doing things."